Electromechanical parking brake systems are adequately known from the prior art. Electromechanical parking brake systems of this type on the one hand ensure a static braking of the vehicle for safe stoppage of said vehicle when stationary and on the other hand ensure a dynamic braking of the vehicle. Both braking functions are provided by an electromechanical parking brake unit which is controlled by way of a control device.
A manual actuation of a control element provided in the vehicle interior preferably triggers a switching element provided in the vehicle interior. By actuating the switching element, at least one electronic control signal is generated, which is supplied to the control device for evaluation purposes. A control and evaluation routine embodied in the control device controls the electromechanical parking brake unit, i.e. activates or releases it for instance.
The decision as to which of the cited braking functions is implemented by the electromechanical parking brake when an electronic control signal of this type is present, i.e. static braking or dynamic braking, is made by means of the control and evaluation routine, namely as a function of the vehicle speed currently prevailing, which is determined by way of a speed sensor system provided in the vehicle.
In practice, the determination of the vehicle speed is however prone to faults or there is a failure of the speed sensor system, as a result of which a defective control of the electromechanical parking brake unit can be produced. Within the scope of the control of the electromechanical parking brake unit, it must be ensured that the electromechanical parking brake unit provides the static brake function in the event of a manual actuation of the control element only when the vehicle is stationary. A triggering of the static brake function while moving would result in a blockage of the wheels of the vehicle for instance, as a result of which the driver could lose control of the vehicle.
With electromechanical parking brake systems known from the prior art, an actuation of the switching element in accordance with a special control pattern is needed in order to display the vehicle state, by means of which the current vehicle state is communicated to the control device by means of the driver. For instance, after actuating the control element, the electromechanical parking brake unit is firstly slowly controlled by means of a dynamic deceleration routine, in order, if necessary, to take account of the available dynamic deceleration instance. If the control element is herewith triggered by the driver, a direct release of the parking brake usually takes place. After activating the parking brake in the dynamic operating mode, a static braking of the vehicle takes place by way of the electromechanical parking brake unit and a locking of the electromechanical parking brake takes place following a predetermined minimum actuation duration of the control element for instance.
With further electromechanical parking brake systems known from the prior art, in the event of a failure of the speed signal, the electromechanical parking brake system is operated in an emergency operation mode, wherein a dynamic brake function is exclusively provided for safety reasons only by means of the electromechanical parking brake unit. If the driver now wishes to safely stop his/her vehicle and a failure exists in the speed signal, this herewith produces a loss of comfort and safety for the driver.